Labile Carbon from Artificial Roots Alters the Patterns of N2O and N2 Production in Agricultural Soils

Labile carbon (C) continuously delivered from the rhizosphere profoundly affects terrestrial nitrogen (N) cycling. However, nitrous oxide (N₂O) and dinitrogen (N₂) production in agricultural soils in the presence of continuous root C exudation with applied N remains poorly understood. We conducted an incubation experiment using artificial roots to continuously deliver small-dose labile C combined with ¹⁵N tracers to investigate N₂O and N₂ emissions in agricultural soils with pH and organic C (SOC) gradients. A significantly negative exponential relationship existed between N₂O and N₂ emissions under continuous C exudation. Increasing soil pH significantly promoted N₂ emissions while reducing N₂O emissions. Higher SOC further promoted N₂ emissions in alkaline soils. Native soil-N (versus fertilizer-N) was the main source of N₂O (average 67%) and N₂ (average 80%) emissions across all tested soils. Our study revealed the overlooked high N₂ emissions, mainly derived from native soil-N and strengthened by increasing soil pH, under relatively real-world conditions with continuous root C exudation. This highlights the important role of N₂O and N₂ production from native soil-N in terrestrial N cycling when there is a continuous C supply (e.g., plant-root exudate) and helps mitigate emissions and constrain global budgets of the two concerned nitrogenous gases.